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Where is fieldbus heading for drives?

20 November, 2019

Fieldbuses give variable-speed drives the ability to control processes rapidly and accurately, while accessing data to determine how applications are performing. ABB’s Liam Blackshaw offers some insights into fieldbus developments for VSDs.

A recent development for VSDs is the ability to accommodate two different types of fieldbus module in one drive. This enables a process to be controlled using the most suitable protocol, while gathering process data via another route.

For instance, a Profibus module and an Ethernet module can run at the same time. The Profibus module is ideal for situations requiring a high degree of predictability, allowing several VSDs to respond at the same time and in the same way. In this case, the command and control fieldbus reacts rapidly and in a synchronised manner. At the same time, the Ethernet module can be used to collect production data to show how the system is behaving.

This two-module arrangement brings a degree of flexibility that was not previously possible. Sending control data and production data through one network can lead to the production data slowing down the control system, resulting in the system not responding or the sheer volume of data being collected interrupting communications.

Now, with option modules, users can connect their VSDs to any industrial network. 

Profibus-DP is the most widely used industrial fieldbus for VSDs. Other protocols include DeviceNet (industrial), CanOpen (automotive and motion), Modbus and LonWorks (building and generic sectors). These protocols can be cheaper to install and are often used in factories to provide IT support. VSDs can be connected onto the same networks, allowing them to be viewed via the Internet, or within an office. Any VSD parameter can be transferred readily between either one of the networks. 

In the past decade, there has been a steady increase in the use of industrial Ethernet. The leading contenders for Ethernet-based protocols are EtherNet I/P, Profinet, EtherCat and Modbus TCP/Bacnet IP.

The dual-module approach means that Ethernet networks can be constructed rapidly and easily, because cabling can be daisy-chained. This eliminates any need for an Ethernet switch to connect VSDs to a network. The two-port approach also maintains communications when the VSD is deactivated.

Using Ethernet for control has only recently become feasible. Previously, synchronised, time-stamped operation was unachievable, resulting in uncertainty about when a VSD would start.

With the new protocols now available, users can capitalise on Ethernet speeds. This, coupled with the reassurance of synchronised and predictable operation, enables true device control over Ethernet instead of merely monitoring behaviour.

ProfiSafe – the safe version of Profibus and Profinet – can also be used to transfer safety signals via fieldbus, rather than using a more expensive hard-wired system.

In future, attention will turn to using wireless technologies – cloud-based or using some other form of media – in conjunction with Ethernet systems. This will open up discussions around data sovereignty: who owns the data? How secure is it? And will it affect safety in any way?

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